For beginners, I recommend the following (in order):

1. The Principles and Practice of Ornamental or Complex Turning,Volume 5 of the Holtzapffel family volumes, by John Jacob Holtzapffel (1843-1897).Modern reprints are available from Albert LeCoff of the Woodturning Center, 42 W. Coulter Street, Philadelphia, PA 19144. (215-844-2188) or the Astragal Press, P.O. Box 239, Mendham, NJ 07945-0239. (201) 543-3045. ISBN 0-486-22965-3. (This is called the "bible" of OT. There are four other volumes, also quite interesting, but not focused on OT.)
2. The Society of Ornamental Turners Bulletin collection on compact disk. Click here to get more information on this fabulous collection of OT information.
3. Ornamental Turning, by J.H. Evans (1903-4). Reprints available from Albert LeCoff of the Woodturning Center, 42 W. Coulter Street, Philadelphia, PA 19144. (215-844-2188) or the Astragal Press, P.O. Box 239, Mendham, NJ 07945-0239. (201) 543-3045. ISBN 1-879335-35-2. (Another very good introductory book.)
4. Ornamental Turnery, by Frank M. Knox (1986). ISBN 0-671-61369-3. (I believe this one is out of print, but you may be able to find one at a used bookseller. A good introduction to ornamental turning, with some easy beginner project plans.)
5. The Lathe and Its Uses, by Lukin (1868). Reprints available from Albert LeCoff of the Woodturning Center, 42 W. Coulter Street, Philadelphia, PA 19144. (215-844-2188) or the Astragal Press, P.O. Box 239, Mendham, NJ 07945-0239. (201) 543-3045. (Another fresh viewpoint -- well, fresh in 1868, but still applicable today.)
6. A Bibliography of The Art of Turning and Lathe and Machine Tool History, by Warren Ogden, John Leggat, and Sydney Abell. Available from Albert LeCoff of the Woodturning Center, 42 W.Coulter Street, Philadelphia, PA 19144. (215-844-2188). (This book exhaustively lists all the other known OT books ever written- mostly out of print, but great finds if you happen upon them).

For more advanced practitioners, I recommend the following, mostly out of print, books:

1. Patterns for Turning, by Elphinstone (1872).
2. Eccentric Spiral Turning, by H.C. Robinson (1906).
3. Eccentric Turning, by Engleheart (1852).
4. Double Counting on the Lathe, by Capt. James Ash (1857).
5. Note on the Epicycloidal Cutting Frame, by Bazley (1872).
6. Index to the Geometric Chuck, by Bazley (1875).
7. Mechanick Exercises, by Joseph Moxon. Available from The Astragal Press, P.O. Box 239, Mendham, NJ 07945-0239. (201) 543-3044.

Finally, one recommendation for Holtzapffel owners. The Pedigree of Holtzapffel Lathes, by Warren Greene Ogden, Jr.is a fascinating study of Holtzapffel company records and painstaking research on the ownership of every lathe the firm produced. Although the information in incomplete and includes some inaccurate statements, the history of many of the lathes is quite impressive. Most of the Holtzapffel lathes were quite expensive in their day (as they continue to be), and were owned by a grand assortment of royalty. Queen Victoria of England, the Archduke Otto von Habsburg of Austria, and assorted counts, dukes, captains, and lords all took their turns at the helm of a Holtzapffel. OT has been quite literally the hobby of nobility! For those Holtzapffel owners wishing to know their lathes pedigree, but lacking this book, fill out my Question and Pedigree form completely, and I will return to you the information contained in the book on your lathe number.

You may be able to find some of these books on the web.

Listed below are several other web sites I've found interesting, and more or less germane to the topic at hand. I'd like to direct particular attention to the only other OT web site I know of, James Harris' OT site. James has expanded on the history of the lathe, and has many pictures of his work and others. Oh, and don't forget to turn off the oven before you get lost in hyperspace.